The present invention relates generally to hydraulic mining tool apparatus and more particularly to an improved hydraulic mining tool apparatus wherein the drill string, which extends from ground surface into the mineral formation, is adapted to be maintained stationary during the mining operation while the mining tool, mounted to the lower end of the drill string, is adapted to rotate within the mineral formation.
In recent years, hydraulic mining tool apparatus has been developed which permits the recovery of subterranean mineral deposits by use of a hydraulic mining fluid. Basically, the prior art hydraulic mining tool apparatus is characterized by the use of a high velocity liquid fluid being discharged directly into the subterranean mineral deposit to dislodge minerals therefrom and form a resultant aqueous slurry which may be pumped upward through the mining tool to ground surface. Examples of such hydraulic mining tools are disclosed in my co-pending patent applications Ser. No. 053,029, filed June 28, 1979 and entitled Down Hole Pump With Bottom Receptor, and Ser. No. 121,712, filed Feb. 15, 1980 entitled Improved Hydraulic Mining Tool Apparatus; the disclosures of which are expressly incorporated herein by reference. Although the prior art mining tool apparatus have proven useful in their general applications, there exists substantial deficiencies associated in their use when utilized for the recovery of unconsolidated mineral formations in deep mining applications.
In contrast to consolidated mineral formations, unconsolidated mineral formations, such as tar sands, are stabilized primarily by the compressive forces generated by the weight of the overburden action upon the formation, with the cementation forces existing between individual sand grains being extremely small in magnitude. As the subjacent portions of such tar sand mineral formations are removed during the hydraulic mining process, the overburden compressive force balance within the mineral formation is disturbed, and due to only minimal cementation forces existing between the individual sand grains, a compaction or cave-in situation may occur whereby the surrounding mineral formation catastrophically falls in and around the drill string and mining tool.
When mining in deep unconsolidated mineral formations (i.e., greater than 300 feet below ground surface), the possibility of such a compaction situation occuring is increased by the frictional drag forces exerted by the rotating mining tool and drill string within the formation. Through prolonged duration, these frictional drag forces disturb the fragile cementation forces existing between the individual sand grains and hence, increase the compressive force imbalance within the the formation. The occurence of a compaction situation in deep mining operations causes substantial pressure to be exerted along the entire length of the drill string which simultaneously generates substantial torque on the mining tool during rotation. These high tortional forces may require the intermittent shut-down of the drilling operation or in extreme instances cause a complete structural failure or twist-off of the mining tool within the formation. As will be recognized, intermittent shut-down reduces operating efficiency while a twist-off condition could result in the mining tool being irretrievabley lost within the mineral formation.
In addition to the compaction and frictional drag force deficiencies associated in the prior art, the use of the hydraulic mining tool apparatus in deep mining applications additionally creates substantial problems in the transport of the mined slurry from the mineral formation upward to ground surface. These transport problems are caused primarily due to the use of jet pump eductor transport mechanisms within the hydraulic mining tools, which are characterized by use of a high velocity liquid stream being discharged upward through a venturi orifice. During the liquid discharge flow through the venturi, suction is developed which serves to pull the mined slurry from the mineral bed through the venturi and upward to ground surface. With specific reference to deep mining applications, the pressure volume and velocity requirements necessary to raise the mined slurry upward to ground surface through such jet pump eductor mechanisms, has necessarily rendered the venturi orifice of the device extremely small, which has severely limited the amount of mined material capable of being transported to ground surface. As is evident, the reduction of the amount of material being transported to ground surface decreases the overall efficiency of the mining operation. Although positive displacement pumps (such as a Moyno pump) have been utilized in an attempt to remedy this situation, the use of such positive displacement pumps has proven unsuccessful due to rock particles and other debris within the slurry becoming lodged within and obstructing the pump within a short period of time.
Thus, there exist a substantial need in the art for an improved hydraulic mining tool apparatus which minimizes the possibility of encountering a cave-in situation within the mineral bed, reduces frictional drag forces exerted upon the mineral bed, and further provides a reliable method of transporting large quantities of mined slurry upward to ground surface from deep mineral bed formations.